The broad and intense use of anti-microbial agents in medical and veterinary care is accelerating the rate at which the target Microbes are developing resistance. Alternative approaches are needed to complement the use of antibiotics in disease treatment. Vaccines constitute such an alternative by allowing our immune system early detection and elimination of pathogens.
The immune system has different, complementary and super-imposed components such as innate anti-microbial molecules, the Complement System, the Humoral and Cellular responses. Humoral immunity relies on antibody production. Immuno-globulins or antibodies are proteins which are the effectors of humoral immunity: they are secreted by so-called B lymphocytes in response to antigen, are released into the body fluids where they directly recognize the antigen to which they were designed to bind. Cellular immunity is mediated by cytotoxic T lymphocytes (CTL) which respond to degraded (peptide) fragments of antigens which appear on the surface of the target cell bound to proteins called class I major histo-compatibility complex (MHC) molecules. Virtually all nucleated cells have MHC I molecules on their surface. Apparently upon turn-over of proteins in the cell, peptide fragments bind to the MHC molecules and are transported to the cell surface hereby marking the cell as “self” i.e. belonging the host. For a foreign antigen of a pathogen, that enters the body, to elicit an immune response, it needs to be recognized by the immune system where it can activate specific B cells by binding to surface immuno-globulins and also needs to be taken up by specialized lymphoid cells that process the antigen and export the fragments to the cell surface in association with a different series of MHC molecules: class II MHC's. Peptides bound to class II molecules are presented to helper T cells which become activated and secrete cytokines such as Inter-leucine 2 (IL-2). Depending on still incompletely understood factors the activated Helper T cells lead, on the one hand to the production of Memory B cells and Ig-secreting plasma cells; on the other hand these Helper T cells can induce proliferation of cytotoxic T lymphocytes. CTL's recognize host cells infected by the pathogen and destroy those cells.
Despite the tremendous positive effect of vaccination on global health care, its potential is far from exploited as for many diseases the use of attenuated or inactivated pathogens as antigen sources has stumbled on production, safety and efficacy issues. Synthetic peptide (subunit) vaccines, based on peptide antigens of pathogens rather than on the entire organism, circumvent most of the weaknesses of attenuated or inactivated pathogen vaccines but have often encountered disappointing results because of different reasons: the peptides may not readily associate with MHC molecules, may have a short serum half-life, or are proteolyses or otherwise cleared before being exposed to antigen-presenting macrophages and monocytes. Today's relatively poor understanding of the parameters required for the engineering of safe but highly immunogenic antigens are the reasons for the continued empirical approach to vaccine development.
The invention provides a novel immunogenic complex offering new possibilities for prophylactic and therapeutic control of microbial pathogens. The Immune Complex comprises specific preparations of ribosomes of micro-organisms (as defined below) and specific microbial cell surface proteins, called adhesins (as defined below). The immunogenic complex of this invention targets mainly the Mucosal Immune System. The Mucosal Immune System is found in the gastrointestinal, uro-genital, and respiratory tract of animals and humans. These tissues are covered with a mucosal surface, mostly covered with a single layer of epithelial cells and under which the mucosal immune tissues lie. The Organized Mucosal-Associated Lymphoid Tissue or O-MALT constitutes the specialized inductive sites of the mucosal immune system; the Diffuse mucosal-Associated Lymphoid Tissue or D-MALT constitutes the dispersed effector sites. Both the O-MALT and D-MALT are separated from mucosal surface antigens by epithelial barriers. The O-MALT, where an immune response is initiated, consists of solitary and aggregated lymphoid follicles underlying the mucosal surfaces. Aggregated lymphoid follicles occur mostly in the naso-pharyngeal tonsils and adenoids and are known as Peyer's patches in the small intestine and equivalent structures in the appendix. Single lymphoid follicles are found along the bronchus and the entire gastrointestinal tract.
Youmans and Youmans proposed the use of ribosome extracts as protective vaccines (Youmans A. S. and Youmans G. P., 1965). Since then experimental vaccines incorporating ribosomal preparations from different bacterial, fungal and protozoan microorganisms have been described. Few of these vaccines have made it beyond the laboratory experiment, probably because the active principles of ribosomal extracts were commonly lost upon preparation, leading to irregular and even contradictory results.
Most classic vaccines are injected and mainly lead to the induction of systemic IgG-type antibodies. The immunogenic complex described here, targets mainly the mucosal immune system and leads to the production of high levels of secreted IgA's besides IgG's. Advantages of delivery to and induction of the mucosal immune system are that injection and its intrinsic dangers are avoided and that the Mucosal Immune System has been shown to be less affected by immune depressing agents such as HIV, chemio- or radio-therapy and is earlier and stronger activated in babies and small children.